Abstract-Quantitative characterization of atherosclerotic plaque composition with standard histopathological methods remains limited to sectioned plaques. Raman spectroscopy enables nondestructive quantification of atherosclerotic plaque composition. We used Raman spectroscopy to study the effects of diet and lipid-lowering therapy on plaque development in apolipoprotein (APO) E*3-Leiden transgenic mice. Raman spectra were obtained over the full width and entire length of the ascending aorta and aortic arch. Spectra were modeled to calculate the relative dry weights of cholesterol and calcium salts, and quantitative maps of their distribution were created. In male mice (nϭ20) that received a high-fat/high-cholesterol (HFC) diet for 0, 2, 4, or 6 months, Raman spectroscopy showed good correlation between cholesterol accumulation and total serum cholesterol exposure (rϷ0.87, PϽ0.001). In female mice (nϭ10) that were assigned to an HFC diet, with or without 0.01% atorvastatin, a strong reduction in cholesterol accumulation (57%) and calcium salts (97%) (PϽ0.01) was demonstrated in the atorvastatin-treated group. In conclusion, Raman spectroscopy can be used to quantitatively study the size and distribution of depositions of cholesterol and calcification in APOE*3-Leiden transgenic mice. This study encourages Raman spectroscopy for the quantitative investigation of atherosclerosis and lipid-lowering therapy in larger animals or humans in vivo. Key Words: atherosclerosis Ⅲ Raman spectroscopy Ⅲ cholesterol Ⅲ calcification Ⅲ lipid-lowering treatment P rogression of atherosclerosis is dependent on the amount of lipids that accumulate in the intima of arteries. 1,2 Several drugs have been developed that successfully lower the plasma cholesterol concentration, thereby reducing the rate of progression of atherosclerosis. 3,4 However, despite the success of these drugs, a considerable number of treated patients will still encounter an ischemic event. To improve management of patients with atherosclerosis, a more thorough understanding of plaque progression and regression in vivo, at the chemical level, is required.Raman spectroscopy is a technique that can provide this kind of information. It provides quantitative information about the molecular composition of a sample and enables the nondestructive examination of small volumes of tissue. 5 A Raman method to quantify the relative amounts of protein, cholesterol, adventitial fat, and calcium salts (CS) in the human coronary artery wall has been developed by Brennan et al. 6 Recently, it was demonstrated that high signal-to-noise Raman spectra can be obtained from the aortic arch and arteries of sheep in vivo, in the presence of blood flow, by using specially designed Raman fiber-optic catheters and a transluminal approach. 7,8 We studied atherosclerotic plaque formation in transgenic mice that were fed a high cholesterol-containing diet. These mice, carrying the dysfunctional apoE variant from patients with a dominantly inherited form of familial dysbetalipoproteinemia (APOE...

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Fluorescent lipid peroxidation products (ceroid) form within the atheroma of an atherosclerotic lesion.At present, the initiation and propagation of such oxidative processes in situ are not well understood, in part because of the insolubility of the ceroid deposits. We investigated the chemical composition of ceroid in human atherosclerotic plaque by combining autofluorescence microscopy and Raman spectroscopy. In eight sectioned human atherosclerotic samples, we located granular and ring-shaped ceroid deposits by autofluorescence microscopy. Subsequently, two-dimensional Raman maps of the ceroid deposits and surrounding non-fluorescent atheroma were acquired at 1 µm resolution. These Raman spectra were subjected to a K-means clustering analysis. By assigning a different color to each cluster, pseudo-color Raman images of the tissue sections were obtained. From these images the clusters belonging to ceroid and the non-fluorescent surrounding tissue were selected. The averaged cluster spectra were analyzed by means of a least-squares fit with the Raman spectra of pure chemical compounds. In addition, the Raman spectra were compared with the Raman spectra of normal and oxidized lipids. Marked differences between the Raman spectra of ceroid and surrounding, non-fluorescent atheroma were observed, amidst large sample to sample variation in chemical composition. Compared with the non-fluorescent tissue, the changes in the Raman spectra of the ceroid deposits could best be explained by larger signal contributions from hemoglobin and cholesteryl esters. We conclude that there is a large heterogeneity in the chemical composition of ceroid. Its composition is largely dependent on the chemical constituents of the surrounding atheroma. Heme or heme degradation products are consistently present in the ceroid deposits. Our results support the hypothesis that iron and heme can form complexes with the intravascular lipoproteins, thereby stimulating oxidation and initiating the formation of ceroid.